1. Field of the Invention
The present invention relates to a data storage system and a method of controlling the same, and, more particularly, to a method of determining and applying an adaptive track zero position, and a disc drive using the same, in which a track zero position is adaptively determined to prevent an actuator arm from contacting an outer disc crash stop (OCS) by considering the eccentricity of a spindle motor shaft in regard to tracks of a disc in an offline servo track writing method.
2. Description of the Related Art
Generally, a hard disc drive is a type of data storage device that contributes to the operation of a system by reproducing data from a disc, or writing data on the disc, using a magnetic head. Recently, in hard disc drives, there has been a trend toward high capacity, high density, and miniaturization. In particular, there has been a trend toward a high recording bit density in a rotation direction (bits per inch, BPI) and in a radial direction (tracks per inch, TPI). Thus, a more sophisticated mechanism to control a hard disc drive is needed.
Related techniques are disclosed in Japanese Patent Publication Nos. 1997-330571 and 1997-128915.
Japanese Patent Publication No. 1997-330571 teaches a method in which an eccentricity is compensated for by measuring a path of rotation of a spindle motor of a disc drive. Japanese Patent Publication No. 1997-128915 teaches a method in which information about an eccentricity with respect to a center of rotation of a disc is stored in a table and then utilized for compensation.
A hard disc drive includes a hard disc assembly (HDA) 10, and a PCB assembly involved in reading and writing operations by controlling the HDA 10. The HDA 10, as shown in FIG. 1, includes a disc 12, a head 20 that writes/reads information on/from the disc 12, a spindle motor 30 that rotates the disc 12, an actuator arm 40 that moves the head 20, a voice coil motor (VCM, not shown), and an outer disc crash stop (OCS) 50 that restricts a displacement of the actuator arm 40.
The OCS 50 is a kind of shock absorber to prevent the head 20 from moving to a non-writable position of the disc 12.
Servo information used to control the head 20 is concentrically recorded on each track of the disc 12 from an outer circumference to an inner circumference of the disc 12. Actually, tracks on which user information is written do not start at a first track, which contains the servo information, but begin with a track that is far from the first track toward the inner circumference of the disc 12, considering a seek overshoot. The section between the physical first track and the actual first track on which the user information is written is called an outer guard band (OGB). Typically, a track 0 (zero) indicates the first track on which the user information can be written. The track number increases from track 0 toward the inner circumference of the disc 12.
The higher the density of the hard disc 12, the more tracks it has, and the more time is consumed by a writing process performed during assembly of the hard disc drive.
To address the problem of the lengthy writing process, a method of assembling a disc drive in which the servo information is written on a hard disc 12 in advance during a manufacturing process has been suggested.
Recording of the servo information onto the disc 12 is referred to as servo track writing (STW), and the method of assembling a disc drive in which the servo information is written on the hard disc 12 in advance during the manufacturing process is called an offline servo track writing (Offline STW) method.
During assembly of the hard disc drive in the Offline STW method, if the center of the disc 12 does not exactly correspond to the axis of rotation of a spindle motor, there may be a difference between a path across the rotating disc 12 of a head 20 following the servo information and an actual rotational path of the disc 12, because the servo information is not written based on the spindle motor 30 operation, but based on the disc 12 operation. The difference of those rotational paths appears in the form of repeatable run out (RRO), which may affect a servo controller as a disturbance, thereby causing a position error signal (PES) to grow abnormally large. In addition, if the difference between the centers of the disc and the rotation axis of the spindle motor is too large, the actuator arm 40 may contact the OCS 50 while following tracks near the outer circumference of the disc 12, thereby causing interference that prevents normal tracking.